Memory device and fabrication method thereof

ABSTRACT

A method of forming a memory device, where a first insulator layer and a charge trapping layer may be formed on a substrate, and at least one of the first insulator layer and charge trapping layer may be patterned to form patterned areas. A second insulation layer and a conductive layer may be formed on the patterned areas, and one or more of the conductive layer, second insulator layer, charge trapping layer and first insulator layer may be patterned to form a string selection line, ground selection line, a plurality of word lines between the string selection and ground selection lines on the substrate, a low voltage gate electrode, and a plurality of insulators of varying thickness. The formed memory device may be a NAND-type non-volatile memory device having a SONOS gate structure, for example.

CROSS-REFERENCE TO RELATED CASES

This is a continuation of U.S. patent application Ser. No. 11/790,047,filed on Apr. 23, 2007 now U.S. Pat. No. 7,538,385, which is acontinuation of U.S. patent application Ser. No. 11/048,852 filed onFeb. 3, 2005, which issued as U.S. Pat. No. 7,223,659 on May 29, 2007,which is a divisional application of U.S. patent application Ser. No.10/382,923 filed on Mar. 7, 2003, which issued as U.S. Pat. No.6,867,453 on Mar. 15, 2005, which is a U.S. nonprovisional patentapplication claiming priority under 35 U.S.C. §119 to Korean PatentApplication No. 2002-0028647, filed on May 23, 2002, in the KoreanIntellectual Property Office (KIPO), the entire contents of all of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a memory device and a fabricationmethod thereof.

2. Description of Related Art

A memory device, such as a non-volatile memory device with a SONOS gatestructure, for example, includes a charge trapping layer which storescharges in an isolated trap within the charge trapping layer. Thenon-volatile memory device may operate at a low operation voltage of5-10V, and may have a simple device structure. Thus, the non-volatilememory device with a SONOS gate structure may be more easily fabricatedin an effort to improve or achieve higher integration within a circuit.

FIG. 1 is a cross-sectional view illustrating a portion of a cell arrayarea of a conventional NAND-type non-volatile memory device.

Referring to FIG. 1, a ground selection line 11G and string selectionline 11S are disposed in parallel on a semiconductor substrate 1. Aplurality of parallel word lines 11W are disposed between the groundselection line 11G and the string selection line 44S. A ground selectiongate insulator 8G is interposed between the ground selection line 11Gand the semiconductor substrate 1, and a string selection gate insulator8S is interposed between the string selection line 11S and thesemiconductor substrate 1. Similarly, a cell gate insulator 8C isinterposed between each of the word lines 11W and the semiconductorsubstrate 1. The cell gate insulator 8C comprises a tunnel insulator 3,a charge trapping layer 5 and a blocking insulator 7 which aresequentially stacked. In addition, the string selection gate insulator8S and ground selection gate insulator 8G have structure identical tocell gate insulator 8C.

Since the string selection gate insulator 8S, ground selection gateinsulator 8G and cell gate insulator 8C of the conventional NAND-typenon-volatile memory device have identical structure, threshold voltagesof a string selection transistor and a ground selection transistor maybe identical with an initial threshold voltage of a cell transistor. Asa result, a voltage, higher than a threshold voltage of a MOS transistorused for a peripheral circuit area should be applied to a stringselection line and a ground selection line in order to turn on thestring selection transistor and ground selection transistor. However,the string selection transistor and ground selection transistor may beweakly programmed when a voltage exceeding threshold voltages of thestring selection transistor and ground selection transistor is appliedto the string selection line and/or the ground selection line. This inturn may cause threshold voltages of the string selection transistor andground selection transistor to increase, leading to higher powerconsumption when driving the string selection transistor and the groundselection transistor.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention is directed to a memorydevice, such as a NAND-type non-volatile memory device, and afabrication method thereof which may provide a string selectiontransistor and a ground selection transistor having a lower thresholdvoltage than in conventional NAND-type non-volatile memory devices withSONOS gate structures, for example.

Accordingly, a memory device in accordance with various exemplaryembodiments of the present invention may include a string selection gateinsulator and a ground selection gate insulator that may be configurableas a single layered blocking insulator, or configurable as adouble-layered structure of a blocking insulator and a tunnel insulator,for example.

An exemplary embodiment is directed to a method of forming a memorydevice, where a first insulator layer and a charge trapping layer may beformed on a substrate, and where at least one of the first insulatorlayer and charge trapping layer may be patterned to form patternedareas. A second insulation layer and a conductive layer may be formed onthe patterned areas, and one or more of the conductive layer, secondinsulator layer, charge trapping layer and first insulator layer may bepatterned to form a string selection line, ground selection line, aplurality of word lines between the string selection and groundselection lines on the substrate, a low voltage gate electrode, and aplurality of insulators of varying thickness. The formed memory devicemay be a NAND-type non-volatile memory device having a SONOS gatestructure, for example.

A NAND-type non-volatile memory device in accordance with anotherexemplary embodiment of the present invention may include a stringselection line and a ground selection line that are substantiallyparallel to each other and cross an active region of a semiconductorsubstrate. The active region may be defined by a field oxide, forexample. A plurality of word lines may be disposed in parallel relationbetween the string selection line and the ground selection line.

A cell gate insulator may be interposed between each of the word linesand the active region, and composed of a tunnel insulator, chargetrapping layer and blocking insulator, for example. These layers may besequentially stacked on the substrate. A string selection gate insulatormay be interposed between the string selection line and the activeregion and a ground selection gate insulator may be interposed betweenthe ground selection line and the active region.

Another exemplary embodiment is directed to a method of fabricating aNAND-type non-volatile memory device, where a tunnel insulator andcharge trapping layer may be sequentially formed on a semiconductorsubstrate. At least the charge trapping layer may be patterned to form acharge trapping layer pattern on the semiconductor substrate. Thepattern may be formed at a specified location or predetermined region ofthe substrate. A blocking insulator and gate conductive layer may beformed on the semiconductor substrate. The gate conductive layer,blocking layer, charge trapping layer pattern and tunnel insulator maybe patterned to form a string selection line, word lines, and a groundselection line which are substantially parallel to each other, and,simultaneously, to form a cell gate insulator interposed between eachthe word lines and the semiconductor substrate, a string selection gateinsulator interposed between the string selection line and thesemiconductor substrate, and a ground selection gate insulatorinterposed between the ground selection line and the semiconductorsubstrate over the semiconductor substrate.

Another exemplary embodiment is directed to a method of forming aNAND-type non-volatile memory device that includes preparing asemiconductor substrate having a cell array area and a peripheralcircuit area. A tunnel insulator and a charge trapping layer may beformed on the semiconductor substrate, and then patterned to form astacked layer that exposes one or more specified regions of the cellarray area and peripheral circuit area. A blocking insulator and a gateconductive layer may be formed on the semiconductor substrate. The gateconductive layer, blocking insulator, charge trapping layer pattern andtunnel insulator pattern may be patterned to form a string selectionline, plurality of word lines and a ground selection line which aresubstantially parallel to each other within the cell array area, to forma low-voltage gate electrode within the peripheral circuit area, and,simultaneously, to form a cell gate insulator string selection gateinsulator and ground selection gate insulator as arranged in theprevious exemplary embodiment, and a low-voltage gate insulatorinterposed between the low-voltage gate electrode and the semiconductorsubstrate.

Another exemplary embodiment is directed to a method of forming aNAND-type non-volatile memory device. The method is similar to theprevious embodiment, but only the charge trapping layer is patterned toform a charge trapping layer pattern at specified locations within thesemiconductor substrate in the cell array area. In this exemplaryembodiment, the tunnel insulator, exposed through the charge trappinglayer, may be patterned to form a tunnel insulator pattern under thecharge trapping layer pattern, which simultaneously exposes a portion ofthe semiconductor substrate in the cell array area and in the peripheralsemiconductor substrate. The semiconductor substrate with tunnelinsulator pattern may be oxidized to form a thermal oxide correspondingto the tunnel insulator on the exposed semiconductor substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will become more fullyunderstood from the detailed description given hereinbelow and theaccompanying drawings, wherein like elements are represented by likereference numerals, which are given by way of illustration only and thusare not limitative of the present invention and wherein:

FIG. 1 is a cross-sectional view illustrating a portion of a cell arrayarea of a conventional NAND-type non-volatile memory device;

FIG. 2 is a top view illustrating a general NAND-type non-volatilememory device in accordance with an exemplary embodiment of theinvention;

FIG. 3 is a flow chart described a method in accordance with anexemplary embodiment of the invention;

FIG. 4 is a cross-sectional view illustrating a NAND-type non-volatilememory device taken along a line of I-I′ of FIG. 2 in accordance with anexemplary embodiment of the present invention;

FIGS. 5A through 5E are cross-sectional views illustrating a method offorming the NAND-type non-volatile memory device of FIG. 4;

FIG. 6 is a cross-sectional view illustrating a NAND-type non-volatilememory device taken along a line of I-I′ of FIG. 2 in accordance withanother exemplary embodiment of the present invention; and

FIGS. 7A through 7E are cross-sectional views illustrating a method offorming the NAND-type non-volatile memory device of FIG. 6.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the present invention are shown. This invention may, however, beembodied in different forms and should not be construed as limited tothe exemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. In the drawings, the thickness of layers andregions are exaggerated for clarity. As used herein, the term “on”, aswhen a layer is described as being “on” another layer, may be defined asbeing directly on the other layer, or on top of the other layer with oneor more intervening layers therebetween. Like numbers refer to likeelements, and the reference characters “A” and “B” represent a cellarray area and a peripheral circuit area, respectively throughout and ineach drawing.

FIG. 2 is a top view illustrating a general NAND-type non-volatilememory device in accordance with an exemplary embodiment of theinvention. In FIG. 2, reference numbers in parentheses representcorresponding elements of FIGS. 4 and 6, respectively.

Referring to FIG. 2, a string selection line SSL (41S, 71S) a groundselection line GSL (41G, 71G) and a plurality of word lines WL (41W,71W) there between are present at a cell array region A. The SSL, theGSL, and the WLs are parallel to one another and cross over an activeregion AR defined by a field oxide FOX. A bit line contact BLC (48, 78)applying a voltage through a bit line BL (51, 81) crossing over thelines such as SSL, GSL and WL are disposed adjacent to the stringselection line. A common source line CSL (45, 75) for grounding isdisposed adjacent to the GSL. On the other hand, a gate electrode G(41L, 71L) is located in an active region AR defined by the FOX (32, 62)at the peripheral circuit area B. A source contact SC (49, 79) and adrain contact DC (50, 80) are located at both sides of the gateelectrode G. A gate electrode GC is connected to the gate electrode G.

FIG. 3 is a flow chart describing a method in accordance with anexemplary embodiment of the invention. Generally, in order to fabricatea memory device in accordance with an exemplary embodiment of theinvention, a number of sequential, but alternating forming and patternprocesses may be required in order to form various layers of the device.For example, and as to be described in more detail below, a firstinsulator layer and a charge trapping layer may be formed (Step S10) ona semiconductor substrate. For example, the first insulation layer maybe formed by coating the substrate with a field oxide to provide anactive region, and thermally oxidizing the field oxide and substrate soas to form a thermal oxide (e.g., SiO₂) as the first insulator layer, ortunnel insulator, on the active region. The charge trapping layer may beformed of silicon nitride (Si₃N₄) by a suitable deposition process, asdiscussed further below. These two layers may be formed sequentially,one layer after the other layer, for example.

The first insulation layer and charge trapping layer may be patterned(Step S20) to provide exposed areas of the active region at specifiedlocations along the substrate. The patterning process may be performedusing a photoresist pattern, as discussed further below. A secondinsulation layer and conductive layer may be formed (Step S30) along thesubstrate and on the patterned areas of the first insulation and chargetrapping layers, by a suitable deposition process, as discussed in moredetail below. The second insulator layer, or blocking insulator, may beformed of a material having a high-k dielectric (e.g., a suitable metaloxide) as to be discussed further below, and the conductive layer may beformed of a suitable polysilicon/metal silicide material, for example.

Referring to FIG. 3, a string selection line, ground selection line, aplurality of word lines provided between the string selection and groundselection lines along the substrate, and a low voltage gate electrodemay be formed (Step S40). These lines and gate electrode may be formedby patterning the conductive layer, second insulator layer, chargetrapping layer and first insulator layer. Simultaneously, a plurality ofinsulators may be formed (Step S50) so as to be interposed between thestring selection line, ground selection line, plurality of word linesand substrate, etc. The plurality of insulators may be of varyingthickness, or have a varying number of layers. For example, one or morecell gate insulators may be formed between the word lines and thesemiconductor substrate; one or more (string or ground) selection gateinsulators may be formed between the string (or ground) selection linesand substrate, and one or more low-voltage gate insulators may be formedbetween the a low-voltage gate electrode and semiconductor substrate, asto be illustrated in further detail below. The cell gate insulator mayconsist of sequentially stacked layers (e.g., first insulation layer,charge trapping layer, second insulator layer), and the selection gateinsulators and low-voltage gate insulator may comprise of only one ofthe layers, such as the second insulator layer (e.g., blockinginsulator) for example. Each of these insulators may be provided atspecified regions along the substrate. Thus, a memory device, such as aNAND-type non-volatile memory device having a SONOS gate structure, maybe provided that operates at a low voltage, so as to reduce powerconsumption in components employing such memory devices. Additionally,since the second insulator layer may be formed of a high-k dielectricmaterial, potential current leakage may be prevented.

FIG. 4 is a cross-sectional view illustrating a NAND-type non-volatilememory device taken along a line I-I′ of FIG. 2.

As illustrated in FIG. 4, a tunnel oxide layer 33, charge trapping layer35, and blocking insulator 37 may be sequentially stacked and interposedbetween a word line 41W and an active region (denoted by dotted line 32a) at a cell array area A of a semiconductor substrate 31. The activeregion may be defined by a field oxide 32, for example. the tunnel oxidelayer 33, charge trapping layer 35 and blocking insulator 37 mayconstitute a cell gate insulator 38W, for example. A blocking insulator37 may be interposed between active region 32 a and a string selectionline 41S, and between active region 32 a and ground selection line 41Gin cell array area A. Blocking insulator 37 may be interposed between agate electrode 41L of a low-voltage transistor and the active region 32b (see dotted line) at a peripheral circuit area B. Blocking insulator37 may be a single-layered structure, and may be embodied as any of astring selection gate insulator 38S, ground selection gate insulator38G, and a gate insulator 38L of a low-voltage transistor, as shown inFIG. 4.

An impurity diffusion layer 43 may be disposed on semiconductorsubstrate 31, such as at both sides of each line (i.e., 41S, 41W and41G) and on either side of gate electrode 41L of the low-voltagetransistor, for example. An interlayer dielectric 47 may be provided onsemiconductor substrate 31. One portion of the impurity diffusion layer43 may be interconnected to a bit line contact 48 penetrating throughinterlayer dielectric 47, as seen in FIG. 4. Another portion of impuritydiffusion layer 43, located on an opposite side of the word lines 41Wfrom an adjacent ground selection line 41G, may be interconnected to acommon source line 45 within interlayer dielectric 47. A portion of theimpurity diffusion layers 43 present in the peripheral circuit area Bmay connect a source contact 49 and a drain contact 50 that penetrateinterlayer dielectric 47. A bit line 51 connecting the bit line contact48 may be provided on interlayer dielectric 47, so as to cross over theword lines 41W, for example. The source contact 49 and drain contact 50may be connected to metal pads 52 and 53 on the interlayer dielectric47, respectively.

The string selection gate insulator and the ground selection gateinsulator in the above exemplary embodiment need not include the chargetrapping layer, thus, a string selection transistor and a groundselection transistor may have a lower threshold voltage as compared to aconventional transistor and may be turned on (energized) with a lowvoltage.

Moreover, the blocking layer may be made of a high-k dielectric materialso that a thickness of the blocking layer may be thicker than that of aconventional blocking insulator, without increasing the voltage requiredfor operation, and so as to reduce or prevent a current leakage.

FIGS. 5A through 5E are subsequent cross-sectional views illustrating amethod of forming a NAND-type non-volatile memory device of FIG. 4.

Referring to FIGS. 5A and 5B, a field oxide 32 may be formed on asemiconductor substrate 31 to define an active region. In FIGS. 5A and5B, the active region may be illustrated generally by dotted line boxesat 32 a and 32 b, for example. The semiconductor substrate 31 and fieldoxide 32 may be thermally oxidized at a temperature of less than 900° C.to form a thermal oxide (i.e., SiO₂) as a tunnel insulator 33. Thetunnel insulator 33 may have a thickness of 20-40 Å, for example.

A silicon nitride (Si₃N₄) may be formed on a the semiconductor substrate31 as a charge trapping layer 35. The charge trapping layer 35 may beformed by low-pressure chemical vapor deposition (LPCVD) process, forexample, or by other deposition processes. The charge trapping layer 35may have a thickness of 50-200 Å, for example. The charge trapping layer35 and tunnel insulator 33 may be successively patterned in activeregion 32 a in cell array area A and in active region 32 b of aperipheral circuit area B (e.g., to provide specific locations where thethermal oxide is exposed. The patterning process may be performed usinga photoresist pattern (not shown) as an etching mask. The patterningprocess may be carried out using a mask oxide that may be formed by aphotoresist pattern, as is known, for example.

Referring to FIGS. 5C and 5D, a blocking insulator 37 may be formed onsemiconductor substrate 31, after the charge trapping layer 35 and thetunnel insulator 33 are patterned, for example. The blocking insulator37 may be formed by an atomic layer deposition (ALD) process or byanother deposition process, for example. The blocking insulator 37 maybe composed of materials having a higher dielectric constant than thatof a silicon oxide (SiO₂), i.e., materials having a dielectric constantgreater than 3.9, and a substantially large energy band gap. Theblocking insulator 37 may be formed of a material selected from Al₂O₃,HfO₂ and Ta₂O₅. When the blocking insulator 37 is formed of aluminumoxide (Al₂O₃), the blocking insulator 37 may be formed to a thickness ofabout 100-300 Å. A conductive layer 41 may be formed on a surface of thesemiconductor substrate 31, as shown in FIG. 5D. The conductive layer 41may be formed of polysilicon and metal silicide, for example.

Referring to FIG. 5E, the conductive layer 41, blocking insulator 37,charge trapping layer 35 and tunnel insulator 33 may be patterned toform a string selection line 41S, ground selection line 41G and wordlines 41W in the cell array area A, and, simultaneously, to form alow-voltage gate electrode 41L in the peripheral circuit region B. Thus,a cell gate insulator 38W may be formed between the word lines 41W andthe semiconductor substrate 31; selection gate insulators 38S and 38Gmay be formed between the selection lines 415 and 41G and thesemiconductor substrate 31; and a low-voltage gate insulator 38L may beformed between the low-voltage gate electrode 41L and the semiconductorsubstrate 31. The cell gate insulator 38W may comprise the tunnelinsulator 33, charge trapping layer 35 blocking insulator 37, in astacked manner, as shown in FIG. 5E. The selection gate insulators 38Sand 38G, and low-voltage gate insulator 38L may be composed of a singlelayer, such as blocking insulator 37.

Although not shown in the drawings, impurity ions may be injected intothe semiconductor substrate 31 to form the impurity diffusion layer 43of FIG. 4, using the word lines 41W, the string selection line 41S, theground selection line 41G, the low-voltage gate electrode 41L and thefield oxide 32 as an ion implantation mask in a subsequent process, forexample. As a result, a string selection transistor, cell transistorsand a ground selection transistor may be formed in cell array area A,and a low-voltage transistor may be formed in the peripheral circuitarea B.

A lower interlayer dielectric (not shown) may be formed on thesemiconductor substrate 31 and transistors. A common source line 45 ofFIG. 4 may be formed in the lower interlayer dielectric, to beelectrically connected to the impurity diffusion layer, as is known. Theimpurity diffusion layer may be embodied as a source region of theground selection transistor. An upper interlayer dielectric (not shown)may be formed on the semiconductor substrate and common source line 45.The bit line contact 48 of FIG. 4 may be configured so as toelectrically connect to impurity diffusion layer 43 of FIG. 4, as isknown. The impurity diffusion layer may be configured as a drain regionof the string selection transistor. The source contact 49 and draincontact 50 of FIG. 4, may be electrically connected to the impuritydiffusion layer 43 through the upper and lower interlayer dielectrics.The impurity diffusion layer 43 may be configured as the source anddrain regions of the low-voltage transistor. A bit line 51 may be formedon the upper interlayer dielectric to connect with the bit line contact48, and metal pads 52 and 53 may be formed to connect to source contact49 and drain contact 50, for example.

FIG. 6 is a cross-sectional view illustrating a NAND-type non-volatilememory device taken along a line of I-I′ of FIG. 2 in accordance withanother exemplary embodiment of the present invention.

Unlike the previous exemplary embodiment, the string selection gateinsulator, ground selection gate insulator and gate insulator of alow-voltage transistor in this exemplary embodiment may be embodied as adouble-layered tunnel insulator and a double-layered blocking insulatorof a memory device such as a NAND-type non-volatile memory device, forexample.

As illustrated in FIG. 6, a tunnel oxide layer 63, charge trapping layer65, and blocking insulator layer 67, which may be sequentially stacked,may be interposed between word lines 71W and an active region (seedotted line box 62 a) in cell array area A of a semiconductor substrate61. These layers may form a cell gate insulator 68W. A field oxide 62may define the active region of the semiconductor substrate 61, as shownby dotted line boxes 62 a and 62 b. A tunnel insulator 63 or 63′ and ablocking insulator 67 may be sequentially stacked and interposed betweenthe active region 62 a and a string section line 71S, and between theactive region 62 a and a ground selection line 71G, respectively. Thesestacked layers may be embodied as a double-layered string selection gateinsulator 68S or ground selection gate insulator 68G in cell arrayregion A, as shown in FIG. 6. Additionally, gate insulator 68L of thelow-voltage transistor may also be of a double-stacked configuration, asshown in peripheral circuit area B of FIG. 6.

Similar to previous exemplary embodiments, an impurity diffusion layer73 and a interlayer dielectric 77, common source line 75 and bit line 81may be provided in cell array area A; and a source contact 79, draincontact 80 and metal pads 82 and 83 may be provided in peripheralcircuit area B, as shown in FIG. 6.

FIGS. 7A through 7E illustrate of forming a NAND-type non-volatilememory device of FIG. 6.

Referring to FIG. 7A, a field oxide 62 may be formed on a semiconductorsubstrate 61 to define an active region. In FIGS. 7A and 7B, the activeregion may be illustrated generally by dotted line boxes at 62 a and 62b, for example. A semiconductor substrate 61 and the field oxide 62 maybe thermally oxidized at a temperature of about 900° C. or less to forma tunnel insulator 63 of silicon oxide (SiO₂). A silicon nitride (Si₃N₄)may formed on a surface of the semiconductor substrate 61 as a chargetrapping layer 65. The charge trapping layer 65 may formed by LPCVDprocess, for example, or by other deposition processes.

Referring to FIG. 6B, the charge trapping layer 65 may be patterned toexpose a portion of a tunnel insulator 63 at a cell array area A and ata peripheral circuit region B. Alternatively, the charge tapping layer65 and the tunnel insulator 63 may be sequentially patterned to exposeportions of active regions 62 a, 62 b at the cell array area A and atthe peripheral circuit region B. By thermally oxidizing the exposedactive regions, a new tunnel insulator 63′ may be formed. For example, athermal oxide is not formed on the charge trapping layer 65 (e.g.,silicon nitride layer) in this exemplary embodiment.

Referring to FIGS. 7C through 7E, a blocking insulator 67 may be formedon an entire surface of the semiconductor substrate 61 by an ALDprocess, for example, or by another known deposition process. Aconductive layer 71 may be provided on semiconductor substrate 61. Theconductive layer 71, blocking insulator 67, charge trapping layer 65 andtunnel insulator 63 may be successively patterned to form a stringselection line 71S, word lines 71W and a ground selection line 71G incell array area A, and, simultaneously, to form a low-voltage gateelectrode 71L on a peripheral circuit area B. As a result, a cell gateinsulator 68W may be formed between the word lines 71W and semiconductorsubstrate 61, and selection gate insulators 685 and 68G may be formedbetween selection lines 71S and 71G and the semiconductor substrate 61.In addition, a low-voltage gate insulator 68L may be formed between thelow-voltage gate electrode 71L and the semiconductor substrate 61. Thecell gate insulator 68W may comprise the tunnel insulator 63, chargetrapping insulator 65 and blocking insulator 67, which may be stacked,as shown in FIG. 7E. The selection gate insulators 68S and 68G may havea double layered structure, as may blocking insulator 67 and tunnelinsulator 63 or 63′, for example.

In each exemplary embodiment, the various forming and patterningprocesses may be used, with materials used for, and thickness of, eachlayer being identical in each exemplary embodiment. Additionally,although specific deposition processes have been described to form oneor more of the layers, it should be understood that other knowndeposition processes, such as CVD, plasma CVD, PVD, metal oxide CVD(MOCVD), etc., could be substituted for the deposition processesdescribed above.

According to the above-described exemplary embodiments, a memory device,such as a NAND-type non-volatile memory device with a SONOS gatestructure, may be operated with a low voltage and with an amplifiedcurrent, since one or more of the string selection gate insulator,ground selection gate insulator in the cell array area, and/or thelow-voltage gate insulator of the peripheral circuit have a single layerconstruction (e.g., single layers blocking insulator), and since theblocking insulator and tunnel insulator may be of a double-layeredconstruction. Additionally, since the blocking insulator may be formedof a high-k dielectric material, any potential current leakage may bereduced and/or completely prevented.

It should be understood that the non-volatile memory device formed inaccordance with exemplary embodiments of the invention is not limited toa NAND-type non-volatile memory device. Other memory devices may beformed in accordance with the exemplary embodiments, including memorydevices have gate structures other than SONOS gate structures.

Exemplary embodiments of the invention being thus described, it will beobvious that the same may be varied in many ways. Such variations arenot to be regarded as a departure from the spirit and scope of theexemplary embodiments of the invention, and all such modifications aswould be obvious to one skilled in the art are intended to be includedwithin the scope of the following, attached claims.

1. A memory device, comprising: a semiconductor substrate comprising acell array area and a peripheral circuit area; a plurality of word lineson the semiconductor substrate of the cell array area; a peripheraltransistor in the peripheral circuit area; a string selection line and aground selection line parallel to each other, the word lines beingbetween the string selection line and the ground selection line; a cellgate insulating layer between the semiconductor substrate and the wordlines, the cell gate insulating layer comprising a first insulatinglayer, a charge trapping layer and a blocking insulating layer, a stringselection gate insulating layer between the semiconductor substrate andthe string selection line, the string selection gate insulating layerthinner than the cell gate insulating layer; and a ground selection gateinsulating layer between the semiconductor substrate and the groundselection line, the ground selection gate insulating layer thinner thanthe cell gate insulating layer, wherein the peripheral transistorcomprises a peripheral gate insulating layer, the peripheral gateinsulating layer including a second insulating layer and the blockinginsulating layer.
 2. The memory device of claim 1, wherein the blockinginsulating layer comprises a material having a dielectric constanthigher than that of silicon oxide.
 3. The memory device of claim 2,wherein the blocking insulating layer comprises metal oxide.
 4. Thememory device of claim 3, wherein the blocking insulating layercomprises at least one of Al₂O₃, HfO₂, and Ta₂O₅.
 5. The memory deviceof claim 1, wherein the charge trapping layer comprises silicon nitride.6. The memory device of claim 1, wherein the first and second insulatinglayers comprise silicon oxide.
 7. The memory device of claim 6, whereinthe first and second insulating layers comprise thermal silicon oxide.8. The memory device of claim 7, wherein the second insulating layer isformed of thermal silicon oxide formed by a process different from thatof the first insulating layer.
 9. The memory device of claim 1, whereineach of the string selection gate insulating layer and the groundselection gate insulating layer consists of a double layer of the secondinsulating layer and the blocking insulating layer.
 10. The memorydevice of claim 1, wherein the charge trapping layer is on a surface ofthe first insulating layer and on a surface of the blocking insulatinglayer.
 11. The memory device of claim 1, wherein the blocking insulatinglayer is a single layer structure.
 12. The memory device of claim 1,wherein the charge trapping layer is comprised of silicon nitride andthe blocking insulating layer is comprised of a metal oxide, the firstinsulating layer being on a surface of the substrate, the chargetrapping layer being on a surface of the first insulating layer and theblocking insulating layer being on a surface of the charge trappinglayer.
 13. The memory device of claim 1, wherein the blocking insulatinglayer is a metal oxide.